Effect of Aqueous Phase Acidity on Thermal and Radiolytic Degradation Behaviour of PUREX Solvent

Reprocessing of fast reactor spent fuels with high Pu content by PUREX process demands high acid extraction condition to avoid the interference of troublesome fission products. Hence, development of process flow sheet under this condition requires the accurate determination of the hydrodynamic properties of the solvent. Towards this, nitric acid induced thermal and radiolytic changes in physico-chemical properties of tri-n-butyl phosphate in n-dodecane were investigated as a function of aqueous phase acid concentrations with respect to time at 40 and 60°C and as a function of absorbed gamma dose up to 20 MRad. Formation of dibutyl phosphate in the thermally degraded solvent suggested that temperature plays a vital role over aqueous phase acidity during degradation. Measurement of zirconium retention by the degraded organic phases revealed that metal retention was significant with increase in the duration of degradation at a particular temperature and acidity or absorbed gamma dose. Washing with alkali to restore the original quality of the solvent was effective to certain extent. Radiolysis of the solvent to the absorbed dose of 20 MRad, at higher acidities resulted in the formation of carboxylic (COOH) and nitro (NO₂) group based compounds, as evident from the FT-IR spectra.